The invention process is concerned with enhancing the recovery of oil from underground formations. More particularly, the invention relates to a method for efficiently producing horizontal wells at their optimum rate of production.
Horizontal wells have been investigated and tested for oil recovery for quite some time. Although horizontal wells may in the future be proven economically successful to recover petroleum from many types of formations, at present, the use of horizontal wells is usually limited to formations containing highly viscous crude. It seems likely that horizontal wells, alone or in combination with standard vertical wells, will soon become a chief method of producing tar sand formations and other highly viscous formations which cannot be efficiently produced by conventional methods because of their high viscosity. Most heavy oil and tar sand formations cannot be economically produced by surface mining techniques because of their formation depth.
Various proposals have been set forth for petroleum recovery with horizontal well schemes. Most have involved steam injection or in situ combustion with horizontal wells serving as both injection wells and producing wells. Steam and combustion processes have been employed to heat the viscous formations to lower the viscosity of the petroleum as well as to provide the driving force to push the hydrocarbons toward a well. Although other forms of enhanced oil recovery such as miscible drive and surfactant processes have been mostly ignored in conjunction with horizontal wells, it is quite possible that horizontal wells will be successful adjuncts to these recovery processes in the future.
The critical velocity concept is described in U.S. Pat. Nos. 3,811,503; 3,878,892; 4,136,738; 4,299,286; 4,418,753; 4,434,852 and Canadian Pat. No. 791,463. U.S. Pat. Nos. 4,257,650 and 4,410,216 discuss horizontal well processes and the critical velocity concept. But these two patents conclude that steam should be injected at rates far above critical velocity in their invention processes because fingering can be tolerated in horizontal well systems.